A record number of Americans ordered holiday gifts online after retailers flooded their inboxes with offers of extra discounts, free shipping and easy returns.

But a storm bringing snow to much of the Midwest on Thursday - the heaviest shipping day of the year - could mean that some packages might not make it under the tree in time for Christmas.

No major disruptions have been reported so far. Wal-Mart said no orders have been delayed. GSI Commerce, which handles online shipping for 70 retailers, said it is monitoring the situation hour-by-hour. So far, deliveries are on time.

Still, the storm's timing couldn't be worse for the world's largest package delivery company, UPS. Before the storm shut down service in some areas, it expected to move 28 million packages on Thursday, nearly double an average day.